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Mar 1, 2002

Getting Enough Blood on the Strip Ensures More Accurate Readings

Do you find yourself squeezing out a huge drop of blood—even for meters that require only a pinpoint of fluid—just to make sure you fill the strip?

Depending on what meter you use, you'll find that if you don't get enough blood on (or in) the strip, you get an error message, waste a strip, and it winds up costing you twice as much to run a test. Or perhaps you'll get an erroneous reading. Or maybe your meter won't start at all.

Why do you need to fill the strip all the way?

To answer that question, you need to know how blood-glucose meters work.

Meters work either by reading the color change on the strip (photometric) or by measuring an electrical current (biosensor).

"Photometric test strips change color as they react to glucose readings in a drop of blood," explains Lia Huse, product manager for Roche Diagnostics in Indianapolis, Indiana. "The meter then measures this color change. With biosensor systems, when you touch your drop of blood to the test strip, it creates a small electrical current. Your meter reads this electrical current and displays your result.

"Both photometric and biosensor systems require enough blood to cover the test area and generate a color change or electrical current."

Therefore, if you don't apply the correct amount of blood to allow the reactions to occur successfully, you're going to get an incorrect result.

Manufacturers take steps to address this issue, although each system on the market operates in a different way.

Huse explains: "With some systems, the test will not begin if enough blood is not applied. With some systems, it will give you an error message. With some systems, it will run the test and potentially provide an inaccurate result."

Roche's Comfort Curve strip, for example, lets you see whether enough blood is on the strip. If that yellow area doesn't turn completely red with the first application, you have 15 seconds to add more blood.

The TheraSense FreeStyle has one channel to wick up the blood, but two electrodes, says Holly Kulp, vice president of professional relations and customer service for the Alameda, California, company.

"It's not until the blood hits that second electrode that [testing] will even start," she explains. "You're not going to short-sample a FreeStyle." Kulp added that the user can continue to add blood to the strip for up to 60 to 90 seconds.

Strips for the new Becton, Dickinson (BD) Logic meter and the BD Latitude Diabetes Management System have two wells to fill and will show an E3 (error) reading if only one has blood in it. It's better to get an error message than to get an inaccurate reading, BD says.

How can you find out how your meter will react if you don't apply enough blood on the strip? Read the owner's manual that came with the meter, or call the manufacturer's customer service center, suggests Huse. The number generally is on the back of your meter.

"Regardless of the situation or the system being used, if a test is run and does not reflect how that person truly feels, they should repeat the test or run a control test before administering therapy," Huse advises.

Categories: Diabetes, Diabetes, Meters

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